This invention relates to disc brakes, and more particularly to monitoring wear of brake linings in disc brakes.
A typical disc brake assembly includes a pair of brake pads that clamp against the surfaces of the brake disc to slow and stop the disc from turning. The pads include an abradable lining that is unavoidably worn away during operation of the disc brake, with the lining eventually being worn away to a point that the pad must be replaced.
The life of the brake lining is directly related to the manner in which the brake is used. The more frequently the brake is applied to slow the disc, and the higher the speed from which the disc must be stopped, the faster the lining will wear. Because the life of the lining is so highly dependent upon the manner in which a particular brake is operated, it is difficult to predict when the linings will need to be replaced. It is desirable, therefore, to provide some means of monitoring the wear of the lining, and enunciating a warning when the lining has worn to a point where it should be replaced.
In many vehicular applications, the brake linings, or the parts supporting the linings, include a metal clip positioned to rub against the disc and generate an audible squeal when the lining has been worn down to the point of needing replacement. Although such a metal clip is effective in some applications, it is sometimes not audible to an operator sitting in the cabin of a vehicle if the cabin is well insulated to attenuate outside noise from entering the cabin. For disc brakes installed on noisy equipment, the squeal of the clip may not be loud enough to be heard over the noise generated by the equipment.
Where such metal clips are ineffective, or for convenience, it is sometimes desirable that the means for monitoring lining wear be adapted to interact with an electronic monitoring circuit capable of providing a visual or audible enunciation that the lining should be replaced.
In one prior system for electrically monitoring lining wear, an electrical terminal, positioned within a brake pad and lining assembly, comes into contact with a rotating surface of the brake disc when the lining has been worn down to a predetermined minimum acceptable lining thickness. Contact of the electrical terminal with the disc creates an electrical ground through the rotating disc that can be detected by an external electrical circuit, and used to change the state of the circuit for illuminating a warning light, or otherwise electrically enunciating a warning that the brake linings need to be replaced.
Reliability of such prior electrical monitoring systems is compromised, however, by reliance upon the need for completing an electrical circuit through contact of the electrical terminal with the surface of the disc, where both the contact and disc are movable, and operating in a severe environment. As the brake is applied, the lining is abraded away and forms dust that can interfere with operation of the monitoring system. The surface of the disc is also worn away, and may become striated or warped, making contact of the terminal intermittent and unreliable. Considerable heat is also generated each time the brake is applied. For vehicular applications, the disc brake assembly may also be exposed to environmental hazards, such as dust, water, salt spray, and mud. What is needed, therefore, is an improved apparatus and method for monitoring wear in a disc brake lining that provides a solution to one or more of the problems described above.
Our invention provides an improved method and apparatus for determining lining wear in a disc brake by monitoring the position of the caliper with respect to the mounting bracket supporting the caliper.
One form of our invention provides a method for sensing lining wear in a disc brake assembly having a rotor disc that is rotatable about an axis and a brake caliper adapted for floating attachment to a mounting bracket in a manner providing limited axial movement of the caliper with respect to the bracket as the lining wears away, by determining a relative axial distance of the caliper from the bracket. Because the relative axial distance of the caliper from the bracket changes as the lining is worn away, the remaining distance between the caliper and the mounting bracket is representative of the remaining thickness of the lining. Where it is desirable to have an external electrical circuit enunciate lining condition, our method may further include initiating a change in electrical state of the electrical circuit indicative of the relative axial distance of the caliper from the bracket.
Our invention may be practiced by attaching a first housing to the mounting bracket, and attaching a second housing to the caliper, with the first and second housings each including a bore facing one another, and aligning the bores with respect to one another along a common translational axis. A plunger is inserted in the bores for movement along the translational axis within the bores in proportion to lining wear, and the remaining lining thickness is monitored by determining a position of the plunger along the translational axis within the bores. The position of the plunger in the bores may be used for initiating a change in electrical state of an electrical circuit indicative of the relative axial distance of the caliper from the bracket.
Our invention may also take the form of an apparatus for sensing lining wear in a disc brake assembly having a rotor disc that is rotatable about an axis and a brake caliper adapted for floating attachment to a mounting bracket in a manner providing limited movement of the caliper with respect to the bracket in a direction parallel to the axis as the lining wears away. The apparatus is adapted for connection to an electrical circuit and includes components for determining a relative axial distance of the caliper from the bracket; and components for initiating a change in electrical state of the electrical circuit indicative of the relative axial distance of the caliper from the bracket.
In one form of our invention, the apparatus includes a pair of fixed electrical contacts adapted for connection to the electrical circuit and a movable electrical contact for connecting the pair of electrical contacts to provide a series electrical circuit through the movable electrical contact.
The apparatus may further include a first housing adapted for attachment to the mounting bracket, and a second housing adapted for attachment to the caliper, with the first and second housings each including a bore facing one another and aligned with respect to one another along a common translational axis. A plunger is disposed in the bores and is movable along the translational axis within the bores. A movable electrical contact may be immovably affixed to the plunger. The plunger may also have an enlarged end thereof disposed within the bore of the second housing, and second housing may include a stop at an end of the bore facing the first housing configured to bear against the enlarged end of the plunger and thereby resist further movement of the plunger along the translational axis toward the first housing. The plunger and bore in the second housing may have a length and depth respectively allowing the plunger to move along the translational axis within the bore from a first position at which the enlarged end of the plunger is not in contact with the stop at the end of the bore, to a second position at which the enlarged end of the plunger contacts the stop. The distance of travel along the translational axis between the first and second positions may be predetermined to be substantially equal to the difference between a lining thickness of a new lining and a minimum recommended lining thickness.
The apparatus may further include components for restraining the plunger within the bore of the second housing against movement along the translational axis until the enlarged end of the plunger comes into contact with the stop in the bore of the first housing at the second position. The restraining components may be configured to allow the plunger to be pulled along the translational axis by further relative movement of the first and second housings away from one another after the enlarged end contacts the stop. Further relative movement of the first and second housings away from one another after the enlarged end of the plunger contacts the stop in the first housing may initiate a change in state of an external electrical circuit.
Where a movable electrical contact is affixed to the plunger, further relative movement of the first and second housings away from one another after the enlarged end of the piston contacts the stop in the first housing may initiate the change in state of the electrical circuit by breaking the series circuit through the movable electrical contact, or alternatively by completing the series electrical circuit through the movable electrical contact. In some forms of our invention the apparatus may also have an additional electrical contact for providing a series circuit relationship with the movable contact indicative of an intermediate lining thickness.
Our invention may also take the form of an apparatus having: a rotor disc that is rotatable about an axis of rotation; a mounting bracket adapted for floating attachment of a brake caliper; a brake caliper adapted to receive the lining and adapted for floating attachment to the mounting bracket in a manner providing limited movement of the caliper with respect to the bracket, in a direction parallel to the axis of rotation, as the lining wears away; a first housing adapted for attachment to the mounting bracket, and a second housing adapted for attachment to the caliper, with the first and second housings each including a bore, the bores being aligned with respect to one another and opening toward one another along a common translational axis; a plunger disposed in the bores and movable along the translational axis within the bores in proportion to lining wear; and components for determining a position of the plunger along the translational axis within the bores. The mounting bracket and caliper may include means for aligning the bores in the first and second housings respectively along the translational axis.
Our invention may be readily adapted for use with prior disc brake assemblies. Because our invention does not rely on making electrical contact with the rotating brake disc, problems associated with electrically monitoring lining wear in prior systems are overcome. Because our invention may be practiced in an apparatus having a housing providing environmental protection for components utilized for determining lining wear and initiating a change in electrical state, reliability is enhanced.
The foregoing and other features and advantages of the invention will become further apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims and equivalents thereof.